Preheat oven to 350°F. Stir in 4 of the crushed Butterfinger fun size candy bars into prepared brownie batter.
Grease a mini muffin pan* with nonstick cooking spray (or line with mini muffin cups. Fill each muffin cup 3/4 of the way and bake for 18-20 minutes, until brownies are just cooked through. Remove from oven and let cool for at least 10 minutes in the muffin pan before removing brownie bites to a cooling rack.
Meanwhile, in a large mixing bowl, beat together cream cheese, peanut butter, and powdered sugar until smooth and fully incorporated. Add cool whip and beat until light and fluffy, scraping down the sides as necessary. Refrigerate for at least one hour.
When ready to serve, pipe peanut butter cheesecake filling onto cooled mini brownie bites using a pastry bag fitted with a wide star tip. Garnish each mini cheesecake with remaining crushed Butterfinger.
*you should have enough batter for 42 brownie bites